Chemical-pulp paper-making process



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Patented Dee. 3t 19%) TQE FRANK A. JOHNSOBL OF BELTS MILLS, NEW YORK, ASSIGNOR OF ONE-FOURTH T0 JOHN H. OGONNELL, or SPRINGFIELD, MASSACHUSETTS, ONE-FOURTH 'ro JOHN D. HASKELL, or rUL'roN, NEW YORK, AND ONE-FOURTH TO DILTS MACHINE wonns, me, or rULroN, ew roan, a conronaxrroN or NEW YORK CHEMICAL-PULP PAPER-MAKING PROCESS The invention relates to chemical pulp paper making processes, and its object is the formulating and practice of a method for producing paper of a high grade, more expeditiously and at less cost than by any I means for the same purpose with which this applicant is acquainted. This could also be termed a process for grinding or hydrating chemical pulp.

Taking What is known as grease proof papers as an example in explaining the ini tent of this invention se :tar as applicant is aware, this paper at present is made in beaters requiring from eight to twelve hours of heating with a stone roll and bedplate in order to produce the super-hydrated characteristics which give the grease proofing qualities. The Same grade of paper is used for making glassine by a super-calendering process which gives the paper gloss and transparency. The paper taken for the example is'made from No. 2 grade Burgess bleached sulphite. That is the commercial designation of this particular pulp. It has been cooked some fourteen hours. The chemical pulp as received'from the pulp mill can either be in the form of dry Sheets approximately thirty-two inches long, or it can be shipped in laps which figure or are treated to be thirty to forty per centum dry. The common method, so far as applicants information extends, is to furnish the pulp directly into the heaters, and to lower the beater roll by degrees to bring about the necessary refinement. This is usually an extended and time-consuming operation when fully carried out. In accordance with the invention of this applicant the laps are charged into the magazineof a pulp grinder, and such magazine may be constructed of special design to accommodate the large size or full size bales. The plunger of the hydraulic cylinder of the grinder may be of fourteen inches diameter, and the hydraulic pressure applied may vary from twenty to eighty pounds to the inch. In the making of grease proof paper this pressure at the cylinder would run between forty and Sixty pounds The pulp is thus held against the grinder stone in the presence of a small spray of wa invention.

pa-per.

Application filed October 15, 1927. Serial No. 226,526.

ter, which produces the super-hydration necessary without prolonged brushing, asis the case when the pulp is acted upon in the beaters. The pulp produced by the grinder is of a diiierent nature from that produced by the beaters with rolls filled with steel or bronze bars, because when the heaters are used the individual fibers are apt to have the ends oi their cells closed by the action of the impulses of the beater roll on the bedplate'. 1 That is to say, the ends of the fibers are found to be flattened down and the cellular structure of the fiber closed at the ends. This prevents the thorough hydrationwhich is necessary to produce the character of stock required in accordance with this invention. For that reason the grinder stone is employed by applicant in carrying out this invention. The grinder stone is equipped with a standard type of sharpener, in order that the surface of the stone may be roughened to any degree demanded, depending upon the nature of the pulp to be produced. It is customary to arrange immediatelybelow the grinder Where the stock discharges from the stone, a sand trap to catch' grit and other heavy particles which must be kept out of this high grade Samples of stock are taken at this point, and tested for freeness. Any standard make of freeness tester may be employed, and on the weight of sheet of grease proof paper mentioned, this test would run from to 80.

The opportunity to almost immediately correct any departure from the desired quality of the paper, by proper attention to pressure, to the abrasive surface of the stone, to the spray of water and other details, at the point where the chemical pulp is ground on the stone, and from which it passes to the being inadvertently lost in the production of inferior paper before the improved quality would come again over the machine. believed that by reason of the testing stated,

It is Y to a standard beater.

the process in accordance with this invention may be made very simple. The pulp is reduced tothe paper-making consistency in the one operationof grinding, and goes thence to the paper machine in an almost constant stream, only a few minutes intervening between the grinding of the pulp and the finishing of the paper. Therefore, when the finished paper fails of the required test, the operator can go at once to the grinder, make the necessary correction, and the improved quality of paper comes right along. In present systems of making paper where the pulp is produced in heating engines, it is the experience of this applicant that sometimes many hours are required to treat the pulp as and to the degree demanded, and paper that fails to test at the finishing end of the paper machine must continue to come for several hours before a correction can be properly made and become effective.

From the grinder the stock is carried over a thickener of any standard design, and

some of the water removed, and from this thickener stock may be conveyed if desired The purpose of the beating at this stage of the process is to permit the colors, alum, size or other substances tobe added to the pulp, and the stock is circulated in a light brushing contact with the hedplate. The action of the beater roll also tends to open up the stock, and about one hours time is necessary to thoroughly work through the color or other substances stated.

The stock is dumped from the beater into a chestwhere it is agitated and kept in a suspended condition. The stock is also usually diluted somewhatat this point. From the agitator chest, the stock is'pumped directly to the screen ahead of the paper machine where oversize fibers, lumps, sand or other foreign bodies are taken out before the paper is finally carried onto the forming wire of the machine. Up to this point only two men on each shift are required to produce the pulp, one of them at the grinder and one at the beater. When this same paper is producedin heaters, .six or eight men would probably be called for to get out the same tonnage.

In carrying the paper over the machine it is necessary to use in this invention more vacuum boxes on the wire, as the actual sheet of paper must be formed quickly. In proceeding in accordance with this invention nine Vacuum boxes are used instead of four,

machine would approximate 250 feet per minute on grease proof paper, and after leaving the machine the paper may be given various degrees of calendering by the use of super-calenders.

The outstanding advantages of this invention are believed to he that the result is more uniform stock by super or extra hydration, and since an accurate ch'eckis practicable and easy by means of the testing stated, less human element enters into the manufacture. Where heaters are used the degree of hydration is usually determined by the,feel of the stock by the beater engineer, and no two beater men have the same feel. Hence, through a twenty-four hour run the same machine is likely to deliver pulp possessing three or four different qualities. Applicant holds that by the practice of this invention more uniform hydration of bone dry stock as well as of wet raw pulp is produced at the grinder, and that the same uniformity cannot be reached by heaters.

Having now described this invention and the manner of working the same, I claim 1. A process for treating chemical pulp for making paper, consisting in subjecting chem ical pulp to a grinding operation as distinguished from a beating action, varying the character of the grinding stones or the equivalent thereof in accordance with the nature and quality of the paper to be produced, applying freeness tests at the point of grinding, varying the pressure of the pulp against the grinders and introducing water in accordance with the requirements of the par-' ticular pulp under treatment and the product desired.

2. A process for treating chemical pulp for making-paper, consisting in subjecting chemical pulp to a grinding operation as distinguished from a beating action, varying the character of the grinding stones or the equivalent thereof in accordance with the nature and quality of the paper to he produced, applying freeness tests at the point of grind ing, varying the pressure againstthe grinders and introducing water in accordance with the requirements of the particular pulp under treatment and the product desired, and forming sheet paper quickly from the treated pulp by increasing the Vacuum acting upon the sheet during its formation.

In testimony whereof I atfixmy signature.

FRANK A. JOHNSON.

with about 5 or 6 inches of vacuum applied., I

and in directing the paper over the presses extreme care must be taken in watching the stretch of the sheet at this point. The paper is run over the driers in the regular 'way, and over one set of calender rolls before going to the reels. The average speed of the 

